Engineers at the California Institute of Technology have demonstrated a nanoscale silicon device that can redirect a beam of light in only 74 femtoseconds, an advance that points toward dramatically faster photonic communications, computing, and sensing technologies.
The device works by using one beam of light to control another. A nanoscale silicon metasurface — an engineered array of structures smaller than the wavelength of light — responds almost instantaneously when struck by a control pulse, changing the direction of a signal beam. The switching time of 74 femtoseconds is roughly 74 quadrillionths of a second, a pace far beyond what conventional electronic components can achieve.
The result matters because the movement of information through optical fiber and inside data centers is increasingly limited not by how fast light travels but by how quickly a signal can be redirected or routed. Electronic switches operate on timescales of picoseconds at best, and often nanoseconds. A device that can steer light in tens of femtoseconds suggests a path toward routing and modulation at rates that approach the fundamental limits of the optical signal itself.
The Caltech team built the device around a silicon metasurface, a flat optical element patterned with features on the nanoscale. Such surfaces manipulate light through their geometry rather than through bulk lenses or mirrors, allowing precise control in a footprint measured in micrometers. Because the material is silicon, the approach is compatible with established semiconductor manufacturing, a factor that could ease the transition from laboratory demonstration to practical photonic chips.
In the experiment, a control beam strikes the metasurface and alters its optical properties for an instant, enough to redirect a separate signal beam. The interaction is ultrafast and reversible, meaning the device can be switched repeatedly rather than acting as a one-time optical element. That combination of speed and reconfigurability is what distinguishes the work from static metasurfaces that shape light in a fixed way.
The potential applications span several fields. In communications, faster optical switching could reduce latency and increase throughput in data centers and long-haul networks, where the conversion of optical signals to electrical ones and back remains a bottleneck. In computing, photonic interconnects that route light on chip could move data between processors with less energy than copper wiring. In sensing, the ability to modulate light at extreme speeds could improve lidar, spectroscopy, and other measurement techniques that rely on precise timing of optical pulses.
The research also fits into a broader push toward all-optical signal processing, in which light controls light without intermediate electronics. Achieving that goal requires materials and structures that respond strongly and quickly to optical fields, and the Caltech device offers evidence that silicon nanostructures can meet both demands at once.
Questions remain about how the device would perform outside the laboratory. Scaling the approach to large arrays, integrating it with existing photonic circuits, and maintaining the ultrafast response under real-world operating conditions are challenges the team will need to address. Energy consumption per switching event and the strength of the control pulse required are also factors that will shape whether the technology reaches commercial systems.
Even so, the demonstration sets a notable benchmark. A switching time of 74 femtoseconds places the device among the fastest reconfigurable optical elements reported, and it does so in a material platform that industry already knows how to manufacture at scale. For researchers working on photonic computing and next-generation communications, that combination of speed and manufacturability is likely to draw attention.
The work was carried out at Caltech, where researchers have been exploring nanophotonic devices that manipulate light at the smallest scales. The findings add to a growing body of evidence that silicon, the material at the heart of the electronics industry, can also serve as the basis for ultrafast optical control.
